1. Technical Field
Embodiments described herein relate to a pretensioner, a seatbelt retractor, and a seatbelt unit that activates the seatbelt retractor.
2. Related Art
Various seatbelt retractors that include a pretensioner have thus far been developed for use in a seatbelt unit provided in a vehicle such as an automobile. The pretensioner is configured so as to rotate a spool of the seatbelt retractor in a direction to retract the seatbelt with a gas generated by a gas generator at an initial stage of an emergency case, to thereby take up the seatbelt around the spool. This action quickly removes slack of the seatbelt and gives higher tension to the seatbelt, thus increasing the restraining force of the seatbelt with respect to the occupant.
An example of conventional pretensioners includes a plurality of force transmission members composed of balls accommodated in a pipe, and the force transmission members are made to move by the pressure of the gas generated by the gas generator inside of the pipe, so as to be pressed against a plurality of pressure-receiving portions formed of a lever of a link gear, so that the spool is made to rotate in the direction to retract the seatbelt by the rotation of the link gear (for example, see JP-A-2001-63520).
In the pretensioner according to JP-A-2001-63520, the pipe includes an hole that allows communication between outside and inside of the pipe, and the hole is blocked by a blocking member. In the case where the gas pressure inside of the pipe excessively increases so as to exceed a predetermined pressure during the operation of the pretensioner, the excessive gas pressure acts to remove the blocking member so as to open the hole, thereby discharging the gas out of the pipe.
Recently, usable parts of vehicles that include a pretensioner that has been activated in an emergency case are required to be recycled. However, in general, a considerable gas pressure resides in the pipe after the pretensioner is activated. Such a residual gas pressure in the pipe makes it difficult to demolish the vehicle to recycle the usable parts. Accordingly, it is necessary to discharge the gas inside of the pipe before demolishing the vehicle.
A technique of discharging the gas out of the pipe is disclosed in JP-A-2001-63520. However, the technique of discharging the gas according to JP-A-2001-63520 is only intended to discharge the gas utilizing the gas pressure when the gas pressure inside of the pipe excessively increases so as to exceed the predetermined pressure. Accordingly, in the case where the gas pressure inside of the pipe has not increased beyond the predetermined pressure during the operation of the pretensioner, the gas pressure resides in the pipe after the operation of the pretensioner is finished, unless a piston is removed from the pipe. Therefore, the technique of discharging the gas according to JP-A-2001-63520 is unsuitable for solving the foregoing problem. When the pretensioner is activated, actually the gas pressure inside of the pipe often remains below the predetermined pressure during the operation of the pretensioner.